Serum creatine kinase isoenzyme MB activity: Evaluation of a kit employing agarose-gel electrophoresis with overlay paper fluorescence scanning

A commercial kit for determining serum creatine kinase isoenzyme MB activity was evaluated. The kit employed agarose-gel electrophoresis followed by incubation of overlay paper on the agarose and then fluorescence scanning of the paper. Within-day coefficients of variation ranged from 24.9% for a specimen with no elevation of MB activity to 6.6% for a specimen with moderately elevated MB activity. The kit appeared to demonstrate MB in all sera and showed higher than expected values in recovery studies. The kit performed in a relatively linear fashion from 50 to 500 I.U./1 total creatine kinase activity. Hemolysis appeared to lower measured MB. For comparison with another method, specimens were also analyzed by microcolumn chromatography, which was found to incompletely separate isoenzymes. The kit produced lower values than microchromatography for specimens with low MB activities and higher values for specimens with elevated MB activities. Patients without corroborative evidence of myocardial injury showed a somewhat hyperbolic relationship between per cent MB and total creatine kinase activity, but MB activity was generally 4 I.U./1 or less. Although the kit had serious laboratory shortcomings, it may be as clinically useful as other methodologies.